Based on comprehensive study of a pit bog on the Rudnya Bay seaside (Zeleny Island) stages of landscape development were reconstructed for the south of Lesser Kuril Ridge when an extensive land bridge connecting South Kuril Is-lands with Hokkaido Island had existed there. Fragmentation of the land bridge was finally finished in the maximal phase of the Middle Holocene marine transgression. This led to isolation of island's flora and fauna. Features of the relief of Lesser Kuril Ridge and increase in oceanic climate troubled migration of species from neighbor territories. Woody vegetation degraded rather quickly. Meadow-marsh landscapes have become predominant. Other factors which affected subsequent development of biotic components are climaticfluctuations, tectonic setting which increased the level of groundwater, tsunami waves, strengthening the role of the cold Oyashio Current and the fall of the volcanic ash of Masu volcano. Changes in the landscapes of the Lesser Kuril Islands are in many respects similar to those on the Nemuro Peninsula (Eastern Hokkaido).